1. Field of the Invention
The present invention relates to the field of earth-boring tools and, more particularly, to core catchers as used in coring tools.
2. Description of the Prior Art
Despite recent advances made with respect to logging and measurements while drilling, the best and primary means presently used in the petroleum industry for ascertaining the nature of the rock formation being drilled is to take a physical core sample. In a typical coring tool, the tool includes a coring bit connected to one or more bit shoes to a coring barrel. The coring barrel includes a mechanism for receiving the core and otherwise performing the required downhole coring operations. Chief among these operations is the seizure and retention of the core in the coring barrel for a retrieval to the well surface.
The prior art has developed a wide variety of core catchers which are installed within the coring tool for securing and retaining the core within the core barrel once it has been cut. In the case where the rock formation is highly consolidated, the core is highly integral, and it is only necessary to break the core from the rock fomration and to jam or wedge the bottom of the core within the coring tool for complete retrieval. Such prior art core catchers are operative by means of a frictional, diametral contact between the cut core and the core catcher. The core catcher allows the core to slide upwardly, but when coring is completed and the core barrel raised, the frictional fit between the core catcher and the core causes the core catcher to be jammed tightly against the core, thereby retaining the core within the tool.
However, in fractured or highly unconsolidated formations, any type of diametral friction, contact or means which might disturb the core composition, as it is being cut and loaded within the core barrel, can seriously and substantially interfere or alter the physical arrangement and configuration of earth materials within the fragmented or unconsolidated core.
Therefore, what is needed is a core catcher capable of retaining a fragmented and unconsolidated core within the tool, yet still comprise a tool which accepts the cut core without any substantial disturbance of the core.